Art of producing coated alloys



Patented Aug. 31, 1937 ART .OF PRODUOIN G COATED ALLOYS Henry F. Schroeder, Milwaukee, Wis.

No Drawing. Application May 15, 1935 1 Serial No. 21,610

4 Claims.

This invention relates to improvements in the art of producing coated alloys.

In recent years color has become an increasingly important factor in effecting the sale of a manufactured article. Formerly the automobile buyer was satisfied to have the door handles and other hardware in the usual nickel or chromium finish. Now, however, the manufacturer is endeavoring to color the interior hardware so that it will match or harmonize with the color of the upholstery. At the present time this is being accomplished by ordinary enameling methods. Surface coatings of this type, however, chip and crack too readily, are not sufficiently durable, and the coating processes are expensive.

Heretofore several common forms of aluminum alloys have been treated with hot water merely to improve the physical properties thereof. These alloys have also been treated by immersion in solutions containing an alkali together with a metallic salt to attempt to produce a color effect.

tions to which the finished product may be subjected. Furthermore, the coating is dull and does not form a uniform glossy protective film for the color.

The present invention is the result of extensive experiments which have shown thatif an alumi-' num alloy is manufactured containing chromium and molybdenum, and if said alloy is polished and then immersed in boiling water, an entirely new type of film is produced on the metal, the

said film being hard, transparent, and glossy in appearance, resistant to corrosion, and being capable of uniting with coloring material added to the water to produce a colored coating which will not fade, which is highly durable, and which has the unusual uniformly glossy appearance of the It is therefore one of the objects of the present invention to produce a coated alloy as above described which alloy has the following desirable properties in addition to those previously mentioned:

' Resistance to chipping and cracking under impact;

Ins'olubility in alcohol, and insolubility in alkalis and dilute acids.

A further object of the invention is to provide an improved method of manufacturing the above alloy.

With the above and other objects in view the invention consists of improvements in the art of producing coated alloy and all its parts and combinations as set forth in the claims, and all equivalents thereof.

In carrying out the improved-method of producing the novel product, an aluminum alloy containing both chromium and molybdenum must be used. The following tabulation discloses the proportions of the various ingredients which it is preferred to employ:

Per cent Aluminum -96 Chromium A trace-10 Molybdenum A trace-5 (1) An alloy consisting of: Per cent Aluminum 85-96 Copper 3-10 Chromium .75-5 Molybdenum .10-5 Titanium .05-1

One example of the preferred amounts of the various ingredients to produce the above alloy is: aluminum 95.10%; copper 3.5%; chromium 1.25%; molybdenum 10%; titanium .05%.

I (2) An alloy consisting of: Per cent Aluminum 76-9730 Molybdenum A trace-5 Chromium A trace-5 Zinc 2-14 One example of the preferred amounts of the various ingredients to produce the above alloy is: aluminum zinc 10%; molybdenum-a trace; chromium-a trace.

Optional: Per cent Titanium .10-.50 Zirconium 10-50 The selected ingredients are mixed together and heated to a suitable temperature to form the alloy and a suitable flux may be utilized in the procedure: The molten mass is kept at a bright red heat at all times and is stirred well before being poured into ingot molds, non-electric heating means being preferably us d.

Inasmuch as the coating is usually desired on some finished article, such as an automobile door handle, the alloy is ordinarily sand cast or die cast to desired form. The castings are then highly polished, this being an essential step in attaining proper results, and are next'racked or suspended in boiling water and permitted to remain in this state for about three hours, although longer or shorter periods may be employed. Generally the longer the immersion the thicker the coating. The temperature may in commercial exploitation of the invention be maintained between 205 and 214 Fahrenheit.

It is found that the method above described will produce an extremely hard, transparent, glossy film on the alloy. A similar result may be obtained by subjecting the polished alloy to the action of steam instead of by immersing the alloyed article in boiling water.

Inasmuch as the film produced by the abovementioned process will have no particular color it is desirable to utilize in the water a. suitable pigment or coloring material. This may be any pigment or coloring material which will adhere to the casting during the boiling process and which will not dissolve or otherwise impair the film being formed.

Certain coloring materials may be applied to the casting prior to immersion in the water, said applied coloring cooperating during the boiling process to form a colored film. The use of certain metallic elements as a coloring agent is very satisfactory. For example, when chromium, preferably in pulverized form, is added to the water it will form a greenish color on the alloy; molybdenum, either in pulverized or solid form, will cause a brownish color; chromium, molybdenum and small pieces of copper added together produce a deep bronze effect; titanium dioxide, :40 commonly, known as rutile, and preferably in powdered form, imparts a tan color to the coating, If the immersion is carried out in a steel tank a very good black color will result, and tantalum preferably in powdered form, results in 45 a very hard and durable iridescent reddish brown color.

The coloring medium is not necessarily limited to metals or metallic compounds inasmuch as certain chemicals such asmercurochromein '50 liquid form and potassium permanganate crystals have been found to impart desirable colors tothe alloy.

Immediately after removal from the boiling liquid the film is relatively soft, and after it has 55 been exposed to air for a few seconds it acquires an extreme hardness and durability. It is therefore important, if a polished surface is to result, that care be exercised to prevent rubbing "against the casting before the coating has had "60 an opportunity to harden in the air.

The above process may also be eifectively employed in coating the alloy in sheet form.

The finished product is very desirable in view of the met that the hard, transparent, glossy film -65 seems to cover the coloring material and thereby protect the latter from fading. The film has an even shiny appearance very similar to enamel,

It will not, however, chip or crack and is therefore considerably more practical for most purposes than ordinary enamel. While it has not been possible to analyze the exact nature of the film, experiments have shown that it will not form unless an aluminum alloy is employed containing chromium and molybdenum. The film because of its durability and hardness also protects the colors against wear and corrosion.

While the treating temperatures herein speci-.

fled, have been found to produce desirable results, it should be understood that it is not desired to limit the scope of this invention to any specific treating temperature. Furthermore, while it is contemplated in most instances to utilize a coloring agent, the film alone without additional coloring material may have utility and it is contemplated that a film produced in this manner is within the scope .of this invention whether or not it is colored. The .term untreated as used in the claims means untreated by anything except materials added for coloring purposes.

Various other changes and modifications may be made without departing from the spirit of the invention and all of such changes are contemplated as may come within the scope of the claims.

What I claim is:-

1. A coated aluminum alloy consisting of aluminum, a trace to 10% of chromium, a trace to 5% of molybdenum, and which alloy may contain relatively small amounts of one or more of the following ingredients: copper, zinc, titanium, silicon, and tantalum, said alloy having a hard, transparent, glossy film thereon formed by subjecting the metal to the action of untreated boiling water or steam.

2. A coated aluminum alloy consisting of aluminum, a trace to 10% of chromium, a trace to 5% of molybdenum, and which alloy may contain relatively small amounts of one or more of the following ingredients: copper, zinc, titanium, silicon, and tantalum, said alloy having a hard, transparent, glossy film thereon formed by subjecting the metal to the action of untreated boiling water or steam containing a metallic coloring material.

3. The method of producing a coated aluminum alloy consisting of forming an alloy which consists of aluminum, a trace to 10% of chromium, and a trace to 5% of molybdenum, and which alloy may also contain relatively small amounts of one or more of the following ingredients: copper, zinc, titanium, silicon, and tantalum, and subjecting the alloy to the action of untreated boiling water.

42 The method of producing a coated aluminum alloy consisting of forming an alloy which consists of aluminum, a trace to 10% of chromium, and a trace to 5% of molybdenum, and which alloy may also contain relatively small amounts of one or more of the following ingredients: copper, zinc, titanium, silicon, and tantalum, and subjecting the alloy to the action of untreated boiling water containing a metallic coloring material.

HENRY F. SCHROEDER. 

